The correct option is (c) 1 and 3 only.
Explanation
Sound waves obey the laws of reflection, similar to light. Multiple reflection of sound occurs when sound waves bounce off surfaces repeatedly. This principle is utilized in various devices to direct sound in a specific direction, amplify it, or confine it within a tube to prevent dissipation.
Statement-wise Analysis:
- 1. Megaphone: Correct. A megaphone (or loudhailer) is a horn-shaped device designed to direct sound in a specific direction without spreading it in all directions. The sound waves produced are confined within the tube and undergo multiple reflections against the inner walls, guiding the sound forward towards the audience.
- 2. Microphone: Incorrect. A microphone is a transducer that converts sound energy (mechanical wave) into electrical energy (electrical signal). It operates on principles such as electromagnetic induction or variable capacitance, depending on the type (dynamic or condenser). It does not function based on the principle of multiple reflection of sound.
- 3. Shehanai: Correct. The Shehanai, like trumpets and other horn-based musical instruments, utilizes a conical tube structure. The sound produced by the vibrating air column undergoes multiple reflections inside the tube, which directs the sound outwards towards the listener and enhances its intensity.
Key Takeaway:
Devices like megaphones, horns, musical instruments (trumpets, shehanais), and stethoscopes operate on the principle of multiple reflection of sound to guide and amplify waves. Microphones are transducers that convert sound to electricity.